Scientists have discovered in a swamp in Guadeloupe the largest known bacterium in the world, which comes in the form of white threads the size of human eyelashes.
About 1 cm long, the strange organism, Thiomargarita magnifica, is approximately 50 times larger than all other known giant bacteria and the first to be seen with the naked eye. Thin white threads are found on the surfaces of rotting leaves of mangrove forests in shallow tropical sea marshes.
The discovery came as a surprise because, according to cellular metabolism patterns, bacteria just don’t have to grow that big. Previously, scientists had proposed an upper possible size limit of about 100 times smaller than the new species.
“To put it in context would be like meeting someone as tall as Everest,” said Jean-Marie Woland, a scientist at Lawrence Berkeley National Laboratory who co-authored the study.
Thiomargarita magnifica has been found to contain three times more genes than most other bacteria. Photo: Vollard et al.
The organism was discovered by Olivier Gross, a professor of marine biology at the Université des Antilles in Guadeloupe, while searching for symbiotic bacteria in the mangrove forest ecosystem.
“When I saw them, I thought, weird,” Gross said. The lab first performed microscopic analyzes to determine that the fibers were single cells. A closer inspection also revealed a strange internal structure. In most bacteria, DNA floats freely inside the cell. Thiomargarita magnifica appears to keep its DNA more organized in membrane-bound compartments throughout the cell. “And that’s very unexpected for a bacterium,” Woland said.
The bacterium has also been found to contain three times more genes than most bacteria, and hundreds of thousands of copies of the genome are distributed in each cell, making it unusually complex.
Scientists are still not sure how bacteria evolved to become so large. One possibility is that he has adapted to avoid predation. “If you get hundreds or thousands of times bigger than your predator, you can’t be eaten by your predator,” Woland said.
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However, becoming large would mean losing some of the traditional benefits of bacteria, including the unique ability to move and colonize new niches. “Leaving the microscopic world, these bacteria have definitely changed the way they interact with the environment,” Woland said.
The bacteria have not yet been found elsewhere – and have disappeared from their original location when researchers recently returned, perhaps because they are seasonal organisms. But in an article published in the journal Science, the authors conclude that the discovery “suggests that larger and more complex bacteria may be hiding from view.”
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